MS Office 2007 mystery

[buildersmate]

I have MS Office Professional 2003 installed. When I attempt to open a document created in Word 2007, the system purports to open Word 2007 (it looks exactly like the 2007 format on the screen), instead of converting the .docx file into something that Word 2003 can read using the file converter programme.

The system attempts to install Word 2007 and asks me for my 25 digit license code (which I have never had) so I have to abort the installation. The only of opening the document is by opening Word 2003 first, then calling up the .docx document.

It is possible that at one time I tried a free trial of Office 2007 - which is why I can see I might have had the file structures at some time. However Office 2007 is not listed in Control Control as one of my installed programmes (so I can't delete it) - only Office 2003. I have tried repairing Office 2003 but that does nothing to help.
How can I get rid of the phantom Office 2007?

[Nibble]

You'll have to download the Word 2007 compatability mode, which converts the .docx files in Word 2007 back to Word 2003 .doc files, which your PC has installed.

[buildersmate]

I already have that installed, Nibble, but thanks for the thought.
I've actually now resolved it - a programme called '2007 Microsoft Office system' was sitting in my list of installed programmes. Inconveniently that appears under '2' and not under 'M' for Microsoft or even 'O' for Office. So in a long list of installed programmes, I didn't spot it. Having deleted it, the problem has gone away.
As to what it is, goodness knows - perhaps it is the umbrella under which the Office suite sit.